Method of casting apertured articles



Oct. 29, 1963 R. s. AMALA METHOD OF CASTING APERTURED ARTICLES 2 Sheets-Sheet 1 Filed April 11, 1960 @waxz i m /a AYYOP/VEY Oct. 29, 1963 R. s. AMALA 3,108,341

METHOD OF CASTING APERTURED ARTICLES Filed April 11, 1960' 2 Sheets-Sheet IN VENT OR.

ig/ward J @WQ/Q rd/ iu ATTORNEY United States Patent Ofi ice 3,108,341 Patented Get. 29, 1963 3,108,341 METHOD GE QASTllNG ARERTURED ARTICLES Raymond S. Arnala Gal; Park, Mich, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Apr. 11, 196i fier. No. 21,506 6 Claims. (til. 22-193) This invention relates to heat exchange apparatus and more particularly to internal combustion engine cylinders, compressor cylinders and the like which include a tubular member and a plurality of axially spaced, radially projecting fins fixed to the member which are adapted to radiate heat and which are provided with bolt holes extending through the fins axially of the member whereby the members are fixed to a housing member or the like.

Air cooled cylinders for use in internal combustion engines, compressor cylinders and the like having relatively thin fins projecting from the cylinder about which a current of air or other gas is caused to flow are well known. Pinned cylinders of this type have been made of ferrous metals, often of cast iron. Often it is desired to fasten such cylinders to an engine block or other housing support by means of bolts which pass through the aligned openings in the fins since it may not be desirable to provide the cylinder with a sufficient thickness of metal to conveniently and suitably support fastening bolts.

Cast iron finned cylinders are preferably cast of a ferrous metal having a chemistry such that the cylinder bores are formed of a cast iron having a type A graphite formation and a uniform structure without rosettes. Fins which are cast integrally with a cylinder of a cast iron of this type tend to have extremities composed of white cast iron and intermediate areas, where it would be normally desired to provide bolt holes, composed of a mottled cast iron. The cast iron could, ofcourse, be inoculated so that the ferrous metal at the'extremities of the fins would be grey iron. However, this would provide an undesirable graphite structure in the cylinder bores. The mottled grey cast iron structure in the fin as described above makes it difiicult to bore or drill openings through the fins. Moreover, it is generally desired that the bolt holes be tapered so as to distribute the pressure of the holding bolt over at least a plurality of fins rather than only the uppermost fin. Because of the mottled grey iron structure of the fins and because of the requirement that the bolt hole he tapered, boring or drilling of the bolt holes in the fins is excessively expensive.

It is the object of this invention to provide a method for casting a cylinder bore having a plurality of cooling fins cast integrally therewith and aligned apertures through the fins. It is a further object of this invention to provide an as-cast cylinder having axially spaced, radially projecting cooling fins cast integrally therewith and having aligned openings axially of the cylinder. A more specific object of the invention is to provide an as-cast cylinder liner having axially spaced, radially projecting cooling fins integrally cast therewith which have axially aligned tapered holes therethrough whereby the cylinder liner may be attached to another object by means of a bolt passing through said openings.

These and other objects are accomplished by first providing a metal pattern having the external shape of one half the finned cylinder liner to be cast and having axially aligned openings in the fins. A metal pin is then inserted through the opening so as to snugly fill the openings. In the preferred embodiment of the invention the aligned openings are of a varying diameter in each sequential fin so as to provide a tapered hole and the pin is tapered so as to snugly occupy the hole through each fin. Next, a shell mold is formed over the pattern including the fins and the projecting pin. The pin end havng the larger diameter is located and exposed by breakmg away the shell mold material therefrom. The pin may conveniently be of sufiicient length so that the ends thereof normally extend beyond the mold surfaces. The pm is then withdrawn from the pattern and mold portrons between the pattern fins. This permits the mold to be removed from the pattern. After stripping the mold from the pattern, a core pin is then inserted in the openmg within the mold previously occupied by the pin. The opposite half of the mold is then made in a like manner. The two shell mold pieces are adhesively bonded or otherwlse fastened together in a well known manner and the finned apertured cylinder of the present invention is cast in a conventional manner.

Other objects and advantages will be apparent from the following detailed description, reference being had to the accompanying drawing in which:

FIGURE 1 is a perspective view of an apertured, finned cylinder of the present invention;

FIGURE 2 is a cross-sectional view of a pattern including an axially aligned opening through the fins thereof and a pin occupying the opening for making one half of a mold; v

FIGURE 3 is a shell mold formed over the pattern;

FIGURE 4 is the shell mold after the pattern has been removed; and

FIGURE 5 is an exploded view of a complete mold forcasting two cylinders simultaneously.

Referring to the drawing, the present invention is concerned with the casting of a finned cylinder such as is shown inFIGURE 1 which consists of a cylinder portion 10, and a plurality of radially projecting, axially spaced, relatively thin, heat radiating fins 12 integrally attached to the cylinder 10. The fins are provided with openings 14 aligned axially of the cylinder adapted to receive a bolt (not shown) whereby the cylinder may be attached to a housing, engine block or the like. Preferably a plurality of such bolt holes are provided spaced symmetrically about the cylinder as shown in FIGURE 1 so that the cylinder is held on its mounting with a uniform pressure. Preferably the bolt holes 14 are of progressively smaller size in each succeeding fin so that a tapered bolt may exert pressure on each fin and thereby distribute the compressive forces over a plurality of fins and to facilitate the mold making procedure.

The process of the present invention involves a pattern and mold making procedure which permits the finned cylinder of FIGURE 1 to be cast. In accordance with the process, a pattern representing one-half of the finned cylinder structure is formed of a suitable metal such as brass. The patter-n structure is shown in cross section in FIGURE 2. This pattern includes a main body portion 16 representing the cylinder wall and bore of the cylinder and the radially extending fins 18. An aligned opening is formed through the fins of the pattern, each of which consists of a plurality of openings 29, 22, 23, etc., which are of reduced size in each succeeding fin so as to form a tapered opening. A tapered metal pin with respect to the pattern 16. The cylinder shown in FIGURE 1 has four spaced bolt'hole openings and accordingly the pattern 16 includes two openings 20, 22, 23, etc., and pins 24.

Next, a shell rnol-d 30 is formed over the pattern of FIGURE 2 as shown in FIGURE 3. Essentially the shell I molding process consists of using a thermosetting resin as a binder for the sand grains to form thin-walled molds having high gas permeability, good surface smoothness and dimensional stability. The molding material is genenally a dry mixture of a major proportion of silica sand and a minor proportion of the thermosetting binder. The resin may be present in the form of a powder admixed with the sand or as a coating on the sand particles. Phenol-formaldehyde and melamine-formaldehyde resins are typical examples of thermosetting binders preferably used. The sand employed is preferably free of metallic oxides, clay, moisture and organic matter.

These sand molds are prepared by applying the dry mixture of sand and resin powder over a pattern which has been heated to a temperature preferably in the range of 250 F. to 350 F. The pattern usually includes gates and runners which are aflixed to the pattern as is well known in the art. The layer of the sand-resin mixture is permitted to rest on the hot pattern for a short period of time. A layer of the mix adheres to the metal surface due to the melting of the resin which entraps the sand with which it is intimately mixed thereby producing pattern detail. The pattern temperatures and the length of time the mold material is allowed to remain in contact with the hot metal pattern surfaces will determine the thickness of the mold. After a mold of a desired thickness has been formed, the closely adherent sand-resin layer is preferably cured by heating the mold in a furnace within a range of about 300 F. to 600 F. for a few minutes while in contact with the metal pattern. In this baking operation the resinous material is converted into a hard, insoluble binder which securely bonds the sand-resin grains together.

A suitable sand-resin mixturefor use in the method of this invention consists of a washed silica sand free of metal oxides, clay, moisture and organic matter having a fineness on the order of about 90 AFS to about 125 AFS which is admixed with a curable thermosetting resin such as phenol-formaldehyde resin in quantities of about 3% to and preferably 4% to 5% by weight of the sand-resin mix. The resin may be mixed in powdered foam with the sand or the sand particles may be coated with liquid resin or the resin dissolved in a suitable solvent as is well known in the art.

The shell mold 30 is formed :as follows. The pattern 16 is heated to a suitable temperature such as 400 F., inverted and fastened upon a turnover box. The box and attached pattern are then inverted to permit the sandresin mix to fall upon the heated metal surface of the pattern and remain on the pattern for a time sufficient to permit a layer of about inch thick to build up on the pattern. The box is then righted to remove the excess sand-resin mix and the pattern with the sand-resin mix layer 30 is removed from the box. In this step the resin of the mix melts sumciently to entrap the sand particles and cause them to adhere closely to each other and to the pattern surface to faithfully conform to dimensions of the pattern. The pattern 1 6 includes a gate and runner (not shown) which are fixed thereto. The character of this gate and runner may be observed by an examination of the completed form of the mold of FIGURE 5 described hereinafter. A mold thickness of about inch has been found satisfactory for the purposes of the present invention. After the inch layer of sand-resin has been formed on the pattern, the resin of the sand-resin layer 16 together with the pattern is inserted in a furnace heated within the range of approximately 300 F. to 600 F. for a time sufficient to cure the resin while in contact with the metal pattern. This baking operation results in the conversion of the resinous material into a hard, insoluble binder which securely bonds the sand-resin grains together.

After removal of the pattern and mold from the curing oven, a portion 32 of the shell mold shown in broken lines in FIGURE 3 is broken away if necessary to expose the large diameter end 2 8 of the pin 24". The pin is then withdrawn and the pattern is stripped from the mold to form the mold shown in FIGURE 4. A core pin 34 of the same configuration as the pattern pin 24, preferably formed of the above-described sand-resin mixture, is then inserted in the opening of the mold previously occupied by the pin 24- to form a complete one half mold, a portion of which is shown in FIGURE 4. A second half mold is prepared in a similar manner and the two parts are glued or otherwise fastened together in a well known manner. Preferably the above-described procedure is employed to form the two-part mold shown in FIGURE 5. This mold includes two mold cylinder cavities 36 and 38 which are connected at the base thereof to a common sprue 40 by the gates 42 and 44. Suitable cores (not shown) of the shape of the cylinder bore are positioned within the mold cavities, the mold is closed and is in a condition to receive molten metal.

Although the present invention has been described in terms of a shell mold which is formed on a hot pattern and cured by heat, it is readily apparent that other methods of forming thin-walled shell-type molds may be employed. For example, a sand-resin mixture of the type disclosed in the copending United States application Serial No. 762,120, filed September 19, 1958, now Patent 3,008,205 issued Nov. 14, 1961, and assigned to the assignee of the present invention which may be cured by an acid gas may be employed. Similarly, the shell mold may be formed by a process such as is disclosed in the co-pending United States application Serial No. 852,311, filed November 12, 1959, now Patent 3,059,297 issued Oct. 23, 1962, and assigned to the assignee of the present invention. In shell mold making procedures described herein, other methods of applying the sand-resin mix to the hot pattern may be employed. Thus, for example, a suitably contoured blowhead may be positioned over the pattern so as to provide an enclosed space having a thickness of approximately inch and the sandresin mixture may be applied over the pattern by blowing in a manner well known in the art.

Various modifications in the arrangement and details of the specific embodiment described and shown will be apparent to those skilled in the art and are contemplated within the scope of the present invention as defined in the appended claims.

I claim:

1. A method of forming a mold for use in casting a tubular article having a plurality of fins projecting radially of said article and being spaced axially thereof at least two of said fins having aligned openings therethrough, the steps comprising providing a metal pattern having an external shape of the finned tubular article to be cast and having axially aligned openings through at least two of the pattern fins, inserting a metal pin through said pat tern fin openings so as to snugly fill the same, forming a shell mold over said pattern, withdrawing said pin from saidpattern openings and said shell mold, stripping said mold from said pattern and thereafter inserting a destructible core pin in said mold to replace said metal pin.

2. A method of forming a mold for use in casting tubu lar heat transfer articles having a plurality of axially spaced fins projecting radially of said article at least two of said fins having aligned openings therethrough, the steps comprising forming a metal pattern having the external shape of one-half the said finned tubular article to be cast therein and having axially aligned openings through at least two of said pattern fins, snugly inserting a metal pin through said pattern fin openings, depositing a layer of a sand-resin molding mixture over said pattern and between said fins, curing the resin to form a shell mold over said pattern, withdrawing said pin from said pattern openings and the adjacent openings formed in said shell mold, stripping said mold from said pattern and thereafter inserting a core pin in said mold to replace said metal pin.

3. A method of making a mold for use in casting acylinder having a plurality of fins projecting radially of the cylinder and being spaced axially thereof at least two of said fins having axially spaced openings therethrouigh, the steps comprising providing a metal pattern having the external configuration of the finned cylinder article to be cast and having axially aligned tapered openings through at least two of said pattern fins adapted to receive a tapered pin, snugly filling said openings by inserting a metal pin therethrough, forming a shell mold over said pattern, Withdrawing said pin from said pattern openings and said mold, shipping said mold from said pattern, and inserting a destructible core pin in said mold to replace said metal pin.

4. A method of making a mold for use in casting a cylinder having a plurality of fins projecting radially of the cylinder and heir! spaced axially thereof at least two of said fins having aligned openings the-rethrough, the steps comprising providing a metal pattern having the external configuration of the finned cylinder article to be cast and having axially align-ed tapered openings through at least two of said pattern fins adapted to receive a tapered pin, snugly inserting a metal pin through said pattern openings, forming a shell mold over said pattern and said pin, withdrawing said pin from said pattern openings, stripping said mold from said pattern, inserting a core pin in said mold to replace said metal pin, forming a second half mold in a like manner, and associating said mold halves to form a completed mold.

5. A method of making a mold for use in casting a cylinder having a plurality of fins projecting radially of the cylinder and being spaced axially thereof a plurality of said fins having openings therethro-ugh, the steps comprising providing a metal pattern having the external configuration of the finned cylinder article to be cast and having axial-1y aligned tapered openings through the fins thereof adapted to receive a tapered pin, snugly inserting a metal pin through said pattern openings so as to snugly fill said openings, applying a layer of a sand curable resin mixture over said pattern and between said fins, curing the resin to form a shell mold over said pattern, withdrawing said pin from said pattern openings, stripping said mold from said pattern, and inserting a core pin in said mold to replace said metal pin.

6. A method of making a mold for use in casting an article having a plurality of members projecting angularly therefirom in spaced relation, at least one or said members having an opening the-rethrough, the steps comprising providing a metal pattern having the external shape of the article to be cast and having an opening through one of said members, inserting a metal pin through said opening so as to snugly fill the same, foiming a shell mold over said pattern and said pin, withdrawing said pin from said pattern opening, stripping said mold from said pattern and thereafter inserting a destructible core pin through said opening.

References Cited in the file of this patent UNITED STATES PATENTS 1,473,366 Walther Nov. 6, 1923 2,062,391 Brown Dec. 1, 1936 2,062,394 Brown Dec. 1, 1936 2,396,363 Du Bois et al. Mar. 12, 1946 2,736,077 Bartlett Feb. 28, 1956 2,837,799 Priebe et al June 10, 1958 2,869,194 Cooper Jan. 20, 1959 2,875,485 Schneider Mar. 3, 1959 2,886,865 Leisk May 19, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 108,341 October 29 E 1963 Raymond S Amala It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 41, for "foam" read form Signed and sealed this 21st day of April 1964.

(SEAL) Attest: ERNEST w SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A METHOD OF FORMING A MOLD FOR USE IN CASTING A TUBULAR ARTICLE HAVING A PLURALITY OF FINS PROJECTING RADIALLY OF SAID ARTICLE AND BEING SPACED AXIALLY THEREOF AT LEAST TWO OF SAID FINS HAVING ALIGNED OPENINGS THERETHROUGH, THE STEPS COMPRISING PROVIDING A METAL PATTERN HAVING AN EXTERNAL SHAPE OF THE FINNED TUBULAR ARTICLE TO BE CAST AND HAVING AXIALLY ALIGNED OPENINGS THROUGH AT LEAST TWO OF THE PATTERN FINS, INSERTING A METAL PIN THROUGH SAID PATTERN FIN OPENINGS SO AS TO SNUGLY FILL THE SAME, FORMING A SHELL MOLD OVER SAID PATTERN, WITHDRAWING SAID PIN FROM SAID PATTERN OPENINGS AND SAID SHELL MOLD, STRIPPING SAID MOLD FROM SAID PATTERN AND THEREAFTER INSERTING A DESTRUCTIABLE CORE PIN IN SAID MOLD TO REPLACE SAID METAL PIN. 